Conventionally, an inner diameter blade slicer, a wire saw, and partly an outer diameter blade slicer are used to cut a mother material in preparing a wafer or a chip as a semiconductor material and an electronic material.
Recently, though an outer diameter of a silicon wafer becomes greater, a technical limit of the outer diameter of the silicon wafer which can be sliced by the inner diameter blade slicer is at 8 inches, and it may be at 6 inches in an aspect of profitability in production.
In comparison with the inner and outer diameter blade slicers, the wire saw can slice a semiconductor ingot to provide a number of wafers, for instance, more than 50 wafers in a case, at one time, so that a through-put is expected to be high in the usage of the wire saw. For this reason, it has been widely used, and it is expected that the wafers will be manufactured by using the wire saw, when a semiconductor ingot having a diameter of 12 inches which will be presumably used with a large quantity in the future will be adopted.
In a wire saw apparatus, generally, a loose abrasive grain slurry-injecting method, in which a piano wire runs in pressure contact with an ingot, and cutting oil ("abrasive grain slurry" hereinafter) consisting of lubricating oil and abrasive grains dispersed therein is injected in contact portions between the piano wire and the ingot, is used.
A reciprocating type of a conventional wire saw apparatus comprises three grooved pulleys each of which has grooves on its outer surface, a wire, wound over the grooved pulleys to run through the grooves of the grooved pulleys, for slicing an ingot to provide wafers, a support base for placing the ingot to be sliced thereon, and an abrasive grain slurry-supplying unit, placed in a triangle space region defined by the three grooved pulleys, for supplying a surface of the ingot with an abrasive grain slurry.
The wire is forced to run in pressure contact with the ingot in the directions of right and left, while the abrasive grain slurry-supplying unit supplies the surface of the ingot with the abrasive grain slurry. Thus, the ingot is sliced to provide a number of wafers at one time by the wire.
Similar to the reciprocating type of the wire saw apparatus, a one-way type of a conventional wire saw apparatus comprises three grooved pulleys each of which has grooves on its outer surface, a wire, wound over the grooved pulleys to run through the grooves of the grooved pulleys, for slicing an ingot to provide wafers, a support base for placing the ingot to be sliced thereon, and an abrasive grain slurry-supplying unit, placed at a position immediately before the wire slices the ingot, for supplying a surface of the ingot with an abrasive grain slurry.
The wire is forced to run in pressure contact with the ingot in one direction right or left, while the abrasive grain slurry-supplying unit supplies the surface of the ingot with the abrasive grain slurry. Thus, the ingot is sliced to provide a number of wafers at one time by the wire.
In the conventional wire saw apparatus, the wire needs having a high tensile strength, because the wire has to be tensed during slicing the ingot to provide the wafers. Therefore, a piano wire, an expensive special alloyed steel wire, a ultra-high strength alloyed wire made in accordance with the adjustment of a metallic crystal structure (disclosed in the Japanese Patent Kokai No. 01-222814), an amorphous alloyed wire, etc. are used for the wire for the wire saw apparatus.
Currently, in the wafers sliced by these wires, a yield of the wafers must be improved in accordance with the decrease of kerf loss to lower production cost. For this purpose, a diameter of the wire must be small to decrease the kerf loss.
Thus, various studies in which the diameter of a conventional wire having the diameter of about 0.16 mm is made small are carried out. At the same time, it is desired that a tensile strength of the wire is increased.
In the conventional wire saw apparatus using the loose abrasive grain slurry, however, there are disadvantages in that a slicing performance is low, because the bite of the abrasive grain slurry into the slicing area of the wire saw is instable, and the yield of the wafers and production performance are decreased in a polishing process following the process of slicing an ingot, because a flaw or defect, what is called "saw mark", is occurred by an instantaneous or partial lack of the abrasive grain slurry.
In the conventional abrasive grain slurry-injecting method, a variety of improvements are executed to increase the production performance, because the bits of the abrasive grain slurry into the wire saw is instable and not effectual. For instance, the variety of improvements are to use:
(1) an element wire which consists of a single metal wire or a stranded wire, having a helical groove formed on its surface [disclosed in the Japanese Utility Model Filing No. 60-21620 (the Japanese Utility Model Kokai No. 61-137421)]; and PA1 (2) A WIREMOND (trademark) which is a diamond saw wire made from a piano wire or a stainless steel wire whose surface layer has been firmly embedded with diamond abrasive grains or SiC abrasive grains by bonding a metal such as melting or plating a metal (disclosed in Sumitomo Electric Report No. 132, 1988, March, pages 118 to 122).
In the conventional abrasive grain slurry-injecting method, however, the helically grooved element wire has a disadvantage in that the occurrence of the "saw mark" can not be prevented perfectly, because the abrasive grain is loose in the slurry.
Further, the WIREMOND has disadvantages in that it is very expensive and not widely used for the industrial purpose, because its production process is very complicated. Though the WIREMOND is formed into a ring wire, what is called "endless wire", by connecting its both ends to evade a problem that the production cost is high, the WIREMOND has disadvantages in that a strength of its connected end portion is not enough, and means of guiding it in the wire saw apparatus are easily worn, because an abrasive grain effect is too high.